E.N.V.I.S. ANTENNA

E.N.V.I.S. ANTENNA

Littlewoods Casino

W2IK's NEW

E.N.V.I.S. ANTENNA - part 1

(Emergency Near Vertical Incident Antenna)

Designed and built by Bob Hejl - W2IK-NNN0KSI NAVMC MARS

see the new MARS/80 meter "high efficiency adapter" plans/page for this antenna following the third construction page

Most NVIS antenna systems consist of some type of dipole antenna positioned at a low height so that it's radiated waveform covers a limited area, usually under 500 miles. This inhibits the reception of unwanted signals such as international broadcasters on 40 meters. (Be aware that just because your dipole is less than 1/4 wavelength above ground doesn't make it an NVIS antenna as it will not exhibit full NVIS characteristics.) Also know that depending on propagation and frequency, NVIS signals may not be generated, HOWEVER, this antenna system should still be used when you wish to communicate with a lower noise floor than conventional antennas. (Lower noise floor means better readability.) Being able to change the height you can change the transmission and reception pattern to maintain emergency communcations while avoiding unwanted signals and noise such as "static crashes" caused by distant lightening. This makes short range communications more reliable than if you used HF vertical antennas. My many field tests, and testing by others, verify this. For best results, ALL communicating stations should use this same type of antenna. Like most NVIS antennas, you'll have to use a tuner to match the antenna and transceiver when operating NVIS as one antenna might be used on frequencies from 3.6 - 7.3 MHZ.. This is my re-designed NVIS antenna system which can be quickly deployed to supply regional communications during an emergency. It was designed to be deployed where there aren't even structures to attach an antenna. You don't need to depend on anything to deploy this antenna. It can also compensate for uneven terrain. It's height above ground level can also be easily adjusted to limit or extend signal range by twisting the three support poles to loosen, change the height of each and twist in the other direction to lock in place. There are much less parts than my first NVIS antenna kit.This is a temporary field antenna setup and should not be thought of as a lasting installation. Make sure you visit all three webpages for the complete plans.

To build this antenna system you will need these parts:

3 - 16 inch sections of 1 1/4 inch PVC pipe

7 - 10 inch stakes (Lowes hardware under the name "Tuff Spike" TS 10)

3 - "Rubbermaid" Extension poles, adjustable (telescoping, twist lock) height 3-6 feet. p/n 57341. Walmart Paint Dept.

4 - 2 inch long 1/4x20 Machine screws and matching nuts.

66 feet insulated, stranded wire 18 gauge.(or about 100 ft if you work mainly lower than 7.2 mhz. see text on page 3)

1 - PVC 1/2" 90 degree elbow 1 - 1/2" PVC tubing 1/2 inch in length

75 feet poly or nylon cord (thinner than 1/4 inch diameter)

1 - SO 239 "barrel" connector

You will also need basic hand tools, hand drill with 1/4 and 1/8 inch bits,

soldering iron, hand rasp or grinder, hacksaw, duct tape and epoxy.

CREATING THE ANTENNA SUPPORT SYSTEM

PIX 2

First, take the three 16 inch long sections of 1 1/4 inch white PVC tubing and de-burr the ends so they are smooth and even. These will be part of the ground peg assemblies. Next take three of the 10 inch stakes and cut off the hook as shown in pix 2. The stakes are slightly wide so they don't fit into the PVC tubing.

Taking a hand rasp (but a bench grinder works better and faster) to remove enough material from the rounded area of the stakes so that they will fit very tightly into the PVC. Reduce the same width on the four cross areas as shown in pix 3 so that the stake will be a tight fit into the PVC tubing to a depth of about 2 1/2 inches. You can see the proper result in pix 4.

On the end of the PVC where you are doing this, taper (bevel) the end down just a bit, again refer to pix 4. The bevel will help when you are pushing the stake assembly deeper into sandy or loose soil. This will leave you with three sets of tightly fitting stakes which are fit into sections of PVC as shown in pix 5. To make sure that the stakes remain attached to the PVC tubes during deployment (the action of staking them into the ground and pulling them out of the ground), drill a 1/4 inch diameter hole in each and install a machine screw and nut, tighten them and seal the nut so it doesn't loosen, as shown in pix 6. make sure that the screw passes through the stake so it stays in place.

These assemblies will hold the three variable height poles in place. They will look like pix 7 when placed in the ground. Install them as deeply as possible. (When you put these in the ground, do so with "conviction" (or use a hammer) so they won't fall and will remain vertical. If any stake should break, it will be easy to replace.

Now take the three telescoping poles and 12 inches from each handle wrap several turns of duct tape as shown in pix 8 and 9 so that they'll slide snugly into the top of the PVC as shown in pix 10. (pix 8 shows only two of the three poles with the duct tape wrap) The poles should fit in without forcing them as they'll need to turn within the PVC to adjust the antenna but they should also be tight enough so they remain vertical yet won't slip out. Drill a 1/4 inch hole through the side of each top black-threaded areas of the telescoping poles. See pix 11.

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PIX 1